Description:
Recent calculations and measurements have revealed unexpected oscillations of the total cross section for excitation in low- to intermediate-energy He{sup 2+} + H collisions. A physical explanation of this behavior is given here stemming from analysis of classical trajectory Monte Carlo simulations, molecular orbital close coupling calculations, and solution of the time-dependent Schroedinger equation on a numerical lattice. These results indicate that the observed behavior should be characteristic of a wide range of reactions in ion-atom collisions.

Description:
Storage rings and Penning traps are being used to study ions in their highest charge states. Both devices must have the capability for ion cooling in order to perform high precision measurements such as mass spectrometry and laser spectroscopy. This is accomplished in storage rings in a merged beam arrangement where a cold electron beam moves at the speed of the ions. In RETRAP, a Penning trap located at Lawrence Livermore National Laboratory, a sympathetic laser/ion cooling scheme has been implemented. In a first step, singly charged beryllium ions are cooled electronically by a tuned circuit and optically by a laser. Then hot, highly charged ions are merged into the cold Be plasma. By collisions, their kinetic energy is reduced to the temperature of the Be plasma. First experiments indicate that the highly charged ions form a strongly coupled plasma with a Coulomb coupling parameter.

Description:
Single photon absorption-single electron detachment from few-electron atomic negative ions was studied. A crossed beam apparatus is being used to perform energy- and angle-resolved photoelectron spectroscopic measurements following photodetachment. Forward-directed electrons were collected and energy analyzed. The kinetic energies and yields of the photoelectrons were obtained by fitting the spectral peaks to Gaussian functions. Electron affinities, asymmetry parameters and cross sections are determined from these measurements. A ratio method in which the cross section for the ion of interest is measured relative to that of a reference ion was used. The study of the photodetachment of Li{sup {minus}} was completed, and attention has turned to the photodetachment of the stable ion B{sup {minus}} and the metastable ion Be{sup {minus}}.

Description:
A small microwave ion source fabricated from a quartz tube and enclosed externally by a cavity has been operated with different geometries and for various gases in a cw mode. This source has been used to generate oxygen ion beams with energy as low as 5.5 eV. Beam energy spread has been measured to be less than 1 eV. By installing different metal plates on the front extraction electrode, metallic ion beams such as (Be, Cu, Al, etc.) can be produced.

Description:
The research on theoretical atomic collisions that was funded at The Pennsylvania State University`s Wilkes-Barre Campus by DOE from 1986 to 1998 was carried out by Winger from 1986 to 1989 and by Winter and Alston from 1989 to 1998. The fundamental processes of electron transfer, ionization, and excitation in ion-ion, ion-atom, and, more recently, ion-molecule collisions were addressed. These collision processes were treated in the context of simple one-electron, quasi-one-electron, or two-electron systems in order to provide unambiguous results and reveal more clearly the collisional mechanisms. Winter`s work generally focused on the intermediate projectile-energy range corresponding to proton energies from about ten to a few hundred keV. In this velocity-matching energy range, the electron-transfer cross section reaches a peak, and many states, including electron-transfer and ionization states, contribute to the overall electron-cloud distribution and transition probabilities; a large number of states are coupled, and therefore perturbative approaches are generally inappropriate. These coupled-state calculations were sometimes also extended to higher energies to join with perturbative results. Alston concentrated on intermediate-energy asymmetric collision systems, for which coupling with the projectile is weaker, but many target states are included, and on high energies (MeV energies). Thus, while perturbation theory for electron transfer is valid, it is not adequate to first order. The studies by Winter and Alston described were often done in parallel. Alston also developed formal perturbative approaches not tied to any particular system. Materials studied included He{sup +}, Li{sup 2+}, Be{sup 3+}, B{sup 4+}, C{sup 5+}, and the H{sup +} + Na system.

Description:
We review some of the recent progress in the studies of alkaline-earth, negative ions. Computations of autodetachment rates, electron affinities and transition wavelengths are discussed and some new and improved results are given.

Description:
A crossed laser-negative ion beams apparatus, situated at Oak Ridge National Laboratory has been used for energy and angle-resolved photoelectron spectroscopic measurements following photodetachment. In the current grant period measurements of the cross sections for photodetaching an electron from the Li{sup {minus}} ion were finished. Measurements of the {sigma}(B{sup {minus}})/{sigma}(Li{sup {minus}}) ratio, with a goal of determining photodetachment cross section for B{sup {minus}}, were started. An investigation of the photodetachment of the metastable ion Be{sup {minus}} also began. Preliminary data on the electron affinity, asymmetry parameter and cross section associated with the photodetachment of Be{sup {minus}} at a photon energy of 2.076 eV is reported.

Description:
We review some of the recent progress in the studies of alkaline-earth, negative ions. Computations of autodetachment rates, electron affinities and transition wavelengths are discussed and some new and improved results are given.

Description:
Real-time detection of beryllium particulate is being investigated by the new technique of laser-induced breakdown spectroscopy. For beryllium detection we monitor the 313.1-nm feature of once ionized beryllium (Be II). Numerous publications describe the technique, our beryllium results, and other applications. Here we summarize the important points and describe our experiments with beryllium.

Description:
An improved version of the radial geometry cesium plasma negative ion source, described by Alton and Blazey, has been designed, evaluated and employed for use during routine operation of the Holifield Heavy Ion Research Facility (HHIRF) tandem accelerator. The mechanical features of the source have been improved to facilitate rapid change of degradable parts such as the sputter probe insulator and cathodes and to provide better thermal isolation of the externally mounted oven from the discharge chamber. The source has demonstrated improved operational stability, higher intensities and increased reliability over its predecessor. Negative ion beams from more than twenty-five elements have been provided for the HHIRF experimental program including several molecular hydride beams from difficult elements such as Be, Mg, Ti, Sc, Nd and Zr. A detailed description of the mechanical features of the source as well as the negative ion yield dependence on certain operational parameters are presented. 9 refs., 5 figs., 1 tab.

Description:
Single photon absorption-single electron detachment from few-electron atomic negative ions was studied. A crossed beam apparatus is being used to perform energy- and angle-resolved photoelectron spectroscopic measurements following photodetachment. Forward-directed electrons were collected and energy analyzed. The kinetic energies and yields of the photoelectrons were obtained by fitting the spectral peaks to Gaussian functions. Electron affinities, asymmetry parameters and cross sections are determined from these measurements. A ratio method in which the cross section for the ion of interest is measured relative to that of a reference ion was used. The study of the photodetachment of Li[sup [minus]] was completed, and attention has turned to the photodetachment of the stable ion B[sup [minus]] and the metastable ion Be[sup [minus]].

Description:
A crossed laser-negative ion beams apparatus, situated at Oak Ridge National Laboratory has been used for energy and angle-resolved photoelectron spectroscopic measurements following photodetachment. In the current grant period measurements of the cross sections for photodetaching an electron from the Li[sup [minus]] ion were finished. Measurements of the [sigma](B[sup [minus]])/[sigma](Li[sup [minus]]) ratio, with a goal of determining photodetachment cross section for B[sup [minus]], were started. An investigation of the photodetachment of the metastable ion Be[sup [minus]] also began. Preliminary data on the electron affinity, asymmetry parameter and cross section associated with the photodetachment of Be[sup [minus]] at a photon energy of 2.076 eV is reported.

Description:
The term level diagrams of the doubly excited quartet systems of the LiI isoelectronic sequence up to Ne VIII are presented. The identifications are based on recent theoretical and experimental work which suggest a revision particularly of the 2s3p/sup 4po/ terms. 11 references.

Filter: Years

This dialog allows you to filter your current search.
Each of the Years listed note their name and the number of records that will be limited down to if you choose that option.
The list can be sorted by name or the count.